configure: Fail if CUDA enabled but not found

Without this patch, configure still passes and enables CUDA, no matter
if it was actually found, breaking the build in case it was not.

configure

@@ -5513,7 +5513,8 @@ enabled avfoundation_indev && { check_lib2 CoreGraphics/CoreGraphics.h CGGetActi
 enabled avisynth          && { { check_lib2 "windows.h" LoadLibrary; } ||
                                { check_lib2 "dlfcn.h" dlopen -ldl; } ||
                                die "ERROR: LoadLibrary/dlopen not found for avisynth"; }
-enabled cuda              && check_lib cuda.h cuInit -lcuda
+enabled cuda              && { check_lib cuda.h cuInit -lcuda ||
+                               die "ERROR: CUDA not found"; }
 enabled chromaprint       && require chromaprint chromaprint.h chromaprint_get_version -lchromaprint
 enabled coreimage_filter  && { check_header_objcc QuartzCore/CoreImage.h || disable coreimage_filter; }
 enabled coreimagesrc_filter && { check_header_objcc QuartzCore/CoreImage.h || disable coreimagesrc_filter; }